1. Technical Field
The present invention relates to the field of synthetic speech generation.
2. Description of the Related Art
Synthetic speech generation is used in a multitude of situations; a few of which include: interactive voice response (IVR) applications, devices to aid specific handicaps, such as blindness, embedded computing systems, such as vehicle navigation systems, educational systems for automated teaching, and children's electronic toys. In many of these situations, such as IVR applications, customer acceptance and satisfaction of a system is critical.
For example, IVR applications can be designed for customer convenience and to reduce business operating costs by reducing telephone related staffing requirements. In the event that customers are dissatisfied with the IVR system, individual customers will either opt out of the IVR system to speak with a human agent, will become generally disgruntled and factor their dissatisfaction into future purchasing decisions, or simply refuse to utilize the IVR system at all.
One reason many users dislike systems that provide synthetically generated speech is that such speech can sound mechanical or unnatural and can be audibly unpleasant, even difficult to comprehend. Unnatural vocal distortions can be especially prominent when the speech generated relates to proper nouns, such as people, places, and things due to the many exceptions to rules of pronunciation that can exist for these types of words. Prosodic flaws in the synthetically generated speech can cause the speech to sound unnatural.
Prosodic characteristics relate to the rhythmic aspects of language or the suprasegmental phonemes of pitch, stress, rhythm, juncture, nasalization, and voicing. Speech segments can include many discernable prosodic characteristics, such as audible changes in pitch, loudness, and syllable length. Synthetically generated speech can sound unnatural to listeners due to prosodic flaws within the synthetically generated speech, such as the speed, the loudness in context, and the pitch of the generated speech.